The ability of alkaline electrolytes to wet a metal surface is one of the major causes of leakage in alkaline galvanic cells. The alkaline electrolyte, by wetting the surface of the metal, can actually "creep" through a sealed metal interface. For this reason elaborate precautions have been made to prevent the electrolyte in an alkaline cell from contacting the interface between a seal and certain metal parts of a seal, such as the metal container and the metal cover of the cell. Typical cell systems where this problem is encountered include silver oxide-zinc cells, nickel-cadmium cells, air-depolarized cells and alkaline manganese dioxide cells. In the prior art it has been a conventional practice to incorporate insulating gaskets between the cell container and cover so as to provide a seal for the cell. Generally, the gasket must be made of a material inert to the electrolyte contained in the cell and the cell environment. In addition, it had to be sufficiently resilient and resistant to cold flow under pressure of the seal and maintain these characteristics so as to insure a proper seal during long periods of storage. Materials such as nylon, polypropylene, ethylene-tetrafluoroethylene copolymer (Tefzel) and high density polyethylene have been found to be suitable as gasket materials for most applications.
However, due to the propensity of alkaline electrolytes, such as aqueous potassium hydroxide and sodium hydroxide solutions, to wet metal surfaces, the use of gaskets, such as nylon, has not completely solved the leakage problem. Unfortunately, electrolyte leakage not only depletes the electrolyte solution from the cell but can also cause a corrosive deposit at the cover-container interface that not only affects the cell's appearance but could also cause damage to the device in which the cell is used. In addition, if leakage occurs while the cell is being transported and stored at a retailer's establishment, then the cell becomes unmarketable, resulting in a total loss.
U.S. Pat. No. 3,922,178 discloses a sealing means for alkaline batteries which comprises the use of a polyamide, specifically a fatty polyamide, as a seal or protective coating to prevent alkaline electrolyte from wetting certain surfaces within the cell.
U.S. Pat. No. 3,713,896 discloses an insulating seal for alkaline cells which consists of a layer of cured epoxy-polyamide resin located and compressed between a metallic container and a metallic cover.
It has been observed that electrolyte leakage occurs primarily at the interface of the gasket (appropriately coated or uncoated) and the cover. Although many types of coatings or layers of various materials such as polyamides, epoxy resins, asphalts and cured epoxy-polyamide resins on gaskets have greatly reduced electrolyte leakage at metal-gasket interfaces of alkaline cells, an object of the present invention is to improve the sealing of such cells by disposing a film of a substituted organosilane at the interface of the cover and coated gasket.
It is another object of the present invention to provide a seal for use at the interface of the container and cover of an alkaline cell which comprises a non-conductive gasket coated with a layer of a polyamide, an epoxy resin, asphalt, or a cured epoxy-polyamide resin and wherein a film of silane is disposed and compressed between the interface of the coated gasket and the cover of the cell.
It is another object of the present invention to provide a seal for electrochemical cells which comprises a non-conductive gasket, such as nylon, coated with a layer of a polyamide, such as a fatty polyamide, disposed and squeezed between the interface of the cover, having thereon a film of silane, and the container of the cell.
The foregoing and additional objects will become more fully apparent with the following description.